1. Field of the Invention
The present invention relates to a camera body, an interchangeable lens, an accessory mounted between the camera body and the interchangeable lens, a camera system, and a method for rewriting information.
2. Description of the Related Art
In a conventional camera system configured to be able to communicate between a camera body and an interchangeable lens, the interchangeable lens has optical specific information stored therein as electronic data. The optical specific information is, for example, data indicating a relationship between an amount of movement of the lens and an amount of movement of focusing, data relating to an amount of correction of focusing, focal distance data, and diaphragm data. By transmitting such specific information to the camera in appropriate timing, operations such as auto focus (AF), auto exposure (AE) are implemented.
A camera may be used by mounting an accessory between the camera body and the interchangeable lens. In such a case, the optical specific information of the interchangeable lens and that of the accessory are different from that of the interchangeable lens alone. Thus, some cameras detect the connection of an accessory by the camera body or the interchangeable lens to correct the optical specific information.
However, if a camera body and an interchangeable lens whose design are old and a newly designed accessory are combined and used, there is an issue that the correction of the optical specific information as described above cannot be made. The words of “old” and “new” design are used in the following sense. More specifically, a case in which an accessory (accessory of new design) that cannot be detected by a conventional camera body or interchangeable lens (a camera body or interchangeable lens of old design) or that has no correction value is newly developed is considered.
To solve the above issue, Japanese Patent Application Laid-Open No. 63-199336 discusses that an accessory includes a central processing unit (CPU) and only necessary communication between a camera and an interchangeable lens is changed in midstream to correct optical specific information by taking the accessory into consideration. Japanese Patent Application Laid-Open No. 2002-341424 discusses that if a system of a camera body and an interchangeable lens is older than an accessory, optical specific information of the interchangeable lens is corrected by the accessory and transmitted to the camera.
It may become necessary to change the optical specific information due to individual manufacturing variation of each of the camera, lens, and accessory. In such a case, due to old or new system restrictions, correction data in the accessory needs to be rewritten. Moreover, to maintain flexibility of the system, it is desirable to be able to update data or firmware inside the accessory even after the accessory is delivered to a user. Further, to perform the above process without a special input terminal or an additional component, it is necessary to operate the accessory via an existing camera mount.
An accessory normally operates only after a camera body and an interchangeable lens are combined and when a user updates firmware, the update may be performed while the lens is mounted.
When communication is performed from a camera to an accessory in a configuration as discussed by Japanese Patent Application Laid-Open No. 63-199336 or Japanese Patent Application Laid-Open No. 2002-341424, information necessary to be corrected is processed inside the accessory and other information is transmitted directly from the camera to the lens. Thus, if, for example, a dedicated command to rewrite information inside the accessory is newly created and transmitted from the camera side, the lens side also receives the command.
However, if the lens side does not understand the command, the whole camera system may be adversely affected by causing a malfunction, for example, movement of a focus lens or a diaphragm or data inside the lens being rewritten.